The greatest collision between a planet and another celestial object ever witnessed by scientists happened in July 1994. For six days, Jupiter was bombarded by pieces of a disintegrated comet named Comet Shoemaker-Levy 9. One after another, more than 20 comet fragments slammed into Jupiter's dense atmosphere at speeds of about 60 kilometers (37 miles) a second, creating enormous fireballs easily visible through telescopes on Earth.
The impacts thrilled planetary scientists and amazed the world. But they also served as a reminder that the solar system can be a dangerous place. Earth, too, has been struck many times in the past by huge objects hurtling down from space. Scientists think that a mammoth collision with a large comet or asteroid about 65 million years ago may have led to the demise of the dinosaurs. And in 1908, more than 2,000 square kilometers (770 square miles) of forest near the Tunguska River in central Siberia were leveled by an immense atmospheric blast caused by an object—probably a meteor—less than 100 meters (330 feet) in diameter.
